1. Field of the Invention
Measurement of gas concentration in flowing liquids.
2. Brief Description of the Prior Art
It is important for both normal process control and identification of unusual conditions that may require shutdown or other special action in oil and geothermal well systems and many chemical processes, to know the concentration of gases in liquid flow. It is difficult to measure mixed gas/liquid flows directly because changes in the relative gas/liquid proportions of such flows are not readily distinguishable from changes in the flow rate. If the gas and liquid portions of a mixed flow are separated, it is difficult to monitor the gas flow directly without introducing temperature or pressure changes that produce erroneous measurements.
In one prior art device for logging the concentration of combustible gases in oil well drilling liquid, for example, gases separated from the drilling liquid are combined with a reference air flow, that is then directed to meters for measurement of the total volume and combustible percentage of the flow. If the air flow is not at the same temperature as the separated gases it will change the temperature and apparent volume of those gases so that subsequent measurements will not be accurate. Because of these difficulties, gas concentrations are now most commonly determined by taking samples of liquids and any gases carried by those liquids to a laboratory for chemical analysis. This requires substantial time, during which there may be temperature and/or pressure changes. And, the chemical tests now used identify only the total quantity of gas contained in a liquid, not the relative portions of dissolved and entrained gases.